Corona ignition device



Sept. 22, 1964 R. s. cATALDo 3,149,620

CORONA IGNITION DEVIGE Filed Feb. 18, 1983 4 AITORNEY United States Patent O Deiaware Filed Feb. 18, 1%3, Ser. No. 259,010 7 Claims. (Cl. 123-148) This invention relates to an ignition device for an internal combustion engine of the reciprocating piston type and, more particularly, to an ignition device which provides a corona discharge.

At the present time non-diesel internal combustion engines of the reciprocating piston type, as a general rule, employ at least one conventional spark plug per cylinder for the purpose of igniting the fuel which is introduced into the combustion Chamber. The Conventional spark plug employs two electrodes between which an extremely high Voltage is applied by means of the distributor system, such that a breakdown of the air between the electrodes occurs with a resulting arc discharge. This arc discharge results in a local ignition of the fuel in the combustion Chamber of the engine from which a fiame front propagates in all directions. It has also been proposed to employ either plural spark plugs or some similar instrumentality to provide two or more points of simultaneous ignition within the combustion Chamber. The intended result of the provision of a plurality or ignition points is to provide more uniform burning of the fuel in the combustion Chamber. However, the use of multiple ignition points naturally produces multiple flame fronts. It has been found that whenever two different fiame fronts come together, pressure exchanges occur due to diiferent local pressures resulting in serious power losses'. Thus, such multiple ignition point schemes may adversely affect the Operating efliciency of a piston engine where rapid and intermittent ignition is required.

The present invention provides for an ignition device which may be used in place of the Conventional spark plug. The use of the present invention, in combination with an internal combustion engine of the reciprocating piston type, will result in a more efiicient utilization of fuel and more uniform combustion of the fuel within the combustion Chamber. This is accomplished by means to provide a Corona type discharge between two electrodes associated with the combustion Chamber of the engine.

The invention further provides an energizing scheme which will result in a very intense corona discharge which is extremely uniform in nature throughout the combustion Chamber. Thus, the present invention provides the advantage of a uniform discharge throughout a substantial porton of the combustion Chamber while still providing a discharge the intensity of which satsfactorily approaches that of the standard spark plug. This is acco-mplished by the provision ofra combustion Chamber of corona forming geometry and being Composed of conductive material such that a porton of the combustion Chamber itself acts' as an electrode. A second electrode of uniform cross-section eXtends substantially through the combustion Chamber. The geomet'ry of the combustion Chamber is such that when voltage pulses of the proper wave form are applied to the uniform second electrode, a non-uniform field pattern exists between the electrodes and a corona discharge occurs uniformly about the second electrode.

T hus, the present invention contemplates the combination of Conductive means to form a combustion Chamber of predetermined geometry for interaction with the piston of a reciprocating internal combustion engine. An elongated cylindrical electrode of uniform cross-section extends through the combustion Chamber and is interconnected with a source of voltage pulses. The geometry of the combustion Chamber and its spatial relation to the elongated electrode is such that when voltage pulses of the proper wave form are applied to the electrodes, a non-uniform field is Produced between the electrodes and the combustion Chamber surface, thus, producing a Corona discharge uniformly about the electrode.

In a preferred form of the invention a substantially cylindrical Chamber of uniform cross-section may be formcd by properly forming in the inner surface of the cylinder head and the top surface of the piston semicylindrical grooves which, when the piston and cylinder heads are in proximity, provide an outer electrode which is concentric with the cylindrical center electrode extending through the combustion Chamber.

The invention may be more readily understood upon reference to the following description of an illustrative embodiment which is to be taken with the accompanying drawings of which:

FIGURE 1 is a Cross-sectional View of a porton of the combustion Chamber of an internal combustion engine employing a form of the present invention;

FIGURE 2 is a top view of a piston and cylinder jacket taken along a line 2--2 of FIGURE 1;

FIGURE 3 illustrates the inner surface of the cylinder head with a form of the present invention associated therewith and is taken along a section line 3-3 of FIGURE 1;

FIGURE 4 is a partia] end view of the electrode arrangement and is taken along a section line 4-4 of FIG- URE 1; and

FIGURE 5 is an illustrative Circuit arrangement which may be used to provide voltage pulses of the proper wave form to the electrodes.

FIGURE 1 shows a finned cylinder head 10 which may be suitably secured to an engine block 12. The block 12 is formed to provide at least one cylindrical Chamber 14 in which a piston may travel. With the cylinder head 10 suitably in a place on the block 12 there is provided above and adjacent the cylindrical Chamber 14 a combustion Chamber generally indicated at 16 which is Communicable with both fuel supply and exhaust valves. A typical valve arrangement is shown in FIGURE 1 to include a port 18 through which the flow of fiuid is Controlled by means of a Valve 20. The Construction of the combustion Chamber 16 immediately above cylindrical Chamber 14 is altered in accordance with the present invention to provide a substantially semi-cylindrical groove 21 which runs from left to right across the combustion Chamber 16 as shown in the drawing. This groove is more clearly seen in FIGURE 3. Suitably disposed adjacent and parallel to the cylindrical groove of the combustion Chamber 16 is an extended Cylindrical electrode 22 having a uniform cross-section. The electrode 22 may be secured in place by means of substantially similar mounting arrangements 24 which are securable to the cylinder head 10 by means of threaded ports 26 on opposite sides of the combustion Chamber 16. The mounting arrangements 24 Comprise an insulative Ceramic body 28 adapted to extend into the port 26 a predetermined distance as dictated by a shoulder porton 30 of a diameter which is larger than that of a narrowed section 32 of the port 26. The insulator body 28 and the electrode 22 which is held thereby is firmly secured in position by means of a locking nut 34, the inner diameter of which is smaller than the shoulder 3d of the insulator v28. The locking nut 34 is threaded complementarily to the por-t 26 and tightening of the nut forces the shoulder 30 firmly against vthe section 32. When properly secured in position the electrode 22 extends through the combustion Chamber 16 such that :znanego it immediately faces the semi-cylindrical groove 21 in a parallel fashion.

The electrode 22 may be connected with a source of high voltage pulses by means of a contact 36 which extencls through the insulator body 28. In the arrangement shown in FIGURE 1 the cylinder head is composed of a highly conductive material such as cast iron or aluminum. Thus, for the purposes of electrical discharge, the inside surface of the cylinder head 10 and, more particularly the surface of the groove 21, serves as a second electrode which is complernentary to the electrode 22.

Referring now to FIGURES 2 and 3, the construction of the internal combustion engine section shown in FIGURE 2 may be more readily realized. As shown in FIGUR 2, the engine block 12 has placed thereon a pad or gasket 37 of the proper geometry to ensure proper sealing between the cylinder head 10 and the engine block 12. Additionally, the block is provided with a plurality of threaded holes 38 which are adapted to receive head bolts. This figure indicates both intake valve 20 and exhaust valve 20'. In FIGURE 2 there is shown within the cylindrical chamber 14 a piston 40 having a semi-cylindrical groove 42 formed therein so as to run substantially across the top surface of the piston 40.

VNote thatv the groove 42 terminates in a position so as to be directly communicated with the fuel intake valve 20.

Referring now to FIGURE 3, the interior construction of the cylinder head 10 is shown in greater detail. cylinderihead 10 may have placed thereon a pad 44 which is complementary to the pad 37 shown in FIGURE 2. The head 10 also has formed therein threaded bolt holes 46, which are located so as to be in a cooperative relation with the bolt holes 38 of the engine block. The cylinder head 10 also has formed therein the usual circular combustion Chamber 16 which conforms to the circular cross-section of the cylindrical Chamber 14 shown in FIGURE l. The chamber 16 includes a lateral portion 50 for communicating the charnber 16 with the valves 20 and 20'. Also clearly shown in FIGURE 3 is the semicylindrical groove 21 which extends substantially across the circular portion of Chamber 16 and into the lateral portion 50. The electrode 22 is shown secured in a position such that it is coaxial With the substantially cylindrical volume which is provided by the grooves 21 and 42 when the cylinder head 10 is properly secured in position on the engine block 12 and the piston 40 is in the top dead center position.

It is apparent, as shown in FTGURE 4, that when the cylinder head 10 is in place on the engine block 12 and 'the piston 40 is inV the top dead center position, the

complementary grooves 21 and 42 will be in face-to-face relation to provide an elongatcd cylindrical charnber which is directly communicable with the intake valve 20'. With the piston in the top-dead center position the electrode 22 is substantially equidistant from Vthe surfaces of grooves 21 and 42. Since the piston 40, as well as the cylinder head 10, is composed of a conductive material, such as cast iron or aluminum, the combination of the electrode 22, the semi-cylindrical groove 42 of the piston 40 and the semi-cylindrial groove 21 of the cylinder head 10 is effective to provide a substantially concentric arrangement of cylindrical electrodes; thatis, electrode 22 is concentric with a cylindrical outer electrode formed by the conductive surfaces of the cylinder head and piston. Accordingly, if a sufficient potential gradient exists between the electrodes, a corona discharge may be produced uniformly about the center electrode 22. It may also be seen that the electric field distribution between the effectively concentric electrodes is highly non-uniform due to the geometry of the outer electrode. That is to say, the electric fiux lines extending radially outward from the The center electrode 22 are at the highest density irnmediately in the vicinity of the electrode 22. This field non-uniforrnity is required for the production of corona since a corona cannot exist where the geometry of two spaced electrodes is such that the field intensity pattern therebetween is uniform.

Considering briefiy the characteristics of a corona discharge, it is well known that in a region characterized by a markedly non-uniform gradient such as that between concentric cylinders, the application of a large voltage to the central electrode causes the surrounding gas to become locally ionized or conducting in the region of greatest field intensity. Since the lregion of greatest field intensity is imrnediately adjacent the small cylindrical electrode, the conductive region surrounding the electrode is said to enlarge the effective diameter of the conductor to the outer regions of the conductive envelope. The boundary of the conductive area is determined by the non-uniformity of the field intensity and will exist at the radial distance at which the field intensity is no longer high enough to establish conductivity. This conductive area is known as a corona. This is to be distinguished from the arcing or breakdown type of conductivity which eXists between the electrodes of a spark plug, for example. The corona typically consists of a great number of extremely short-lived luminous fiows of charge which are known as streamers.

Considering the arrangement shown in FIGURES 1 through 4, assume that the piston 40 is in the top dead center position, such that the concentric arrangernent of electrodes is provided. Upon the application of a large negative voltage pulse to the center electrode 22 there will exist in the area surrounding the electrode 22 a unif form volume of negativc space charge. It is to be understood that the magnitude of the voltage pulse applied to the electrode 22 is not such that atrcing Will occur between the electrode 22 and the surface of the chamber 16. It should be noted that even in a corona forming geometry, such as that provided by the present electrode arrangement, arcing or flashover may occur at a sutficiently high voltage. With Vthe application of the voltage pulse the current streainers are produced and extend radially outward from the electrode 22 toward the cylindrical outer electrode provided by the piston 40 and cylinder head 10. The

propagation Velocity of the current streamers is influenced by the rise time of the voltage which is applied to the electrode 22. If the voltage pulse is abrnptly terminated with a fall time substantially less than the lifetirne of a current Streamer, it will be seen that the charge in the space intermediate the concentric electrodes will be immediately attracted back to the now more positive cener electrode 22. In this manner, it may be seen that an extremely Vsquare or Vrectangular input voltage pulse may produce an extreinely high intensity corona discharge. `rfidditionally, this corona discharge Will be highly uniforrn about the electrode 22 and will not result in any localized corona or arcing between the electrodes.

An input voltage pulse having the desired characteristics of rectanguiarity may he produced by the circuit which is schematically indicated in FIGURE 5. This circuit comprises a source 52 of D.C. power, which may com- 'prise a vehicle battery. The source 52 is interconnected with a transistor inverter circuit 54 which is adapted to produce a high voltage amplification from the D.C. source 52. The output of the inverter 54 is interconnected with a switch 56, which includes a pair of contacts 58 and 60 and an armature 62, which is adapted to engage either of the contacts 50 or 60. Contact 60 ofithe switch 56 is interconnected with a pulse forming network 64, the output of which is connected to a primary coil 66. A secondaryV coil 68 is shown magnetically interconnected with the primary coil 66 and is electrically connected with :the electrode 22 of the corona discharge device which is generally designated at 70.

The Varmature 62 is connccted to a capacitor 72 which may be charged by the inverter 54.

Considerng thecircuit Vof FTGURE 5 in greater detail, it may be seen that when the armature 62 engages contact 58, the high voltage output of the transistor inverter 54 is effective to charge the capacitor 72 to a high voltage. When the piston 49 of the internal combustion engine has reached the preferred ignition point, means not shown, may be interconnected with the switch 56 to move the armature 62 into engagement with the contact 60. At this time the capacitor 72 is provided with a discharge path through the pulse forming network 64 which is seen to comprise an inductor 74 connected in series with the parallel combination of an inductor 76 and a capacitor 78. Discharging the capacitor 72 rapidly through the pulse forming network 64 is effective to produce an output voltage pulse across the secondary coil 68 which is rectangular in Wave form. It may be desirable to produce a number of voltage pulses across the electrode 22 during each ignition period and switch 56 will be operated accordingly. The magnitude of the voltage pulse which is applied to the electrode 22 may range, for example, between ten or twelve kilovolts. This figure is, of course, subject to Variation, due to such factors as the spacing between the electrode 22 and the walls of the cylindrical combustion chamber 16. The rise time of the voltage pulse applied to electrode 22, as well as the fall time thereof, should be of a shorter duration than 'the lifetime of a current Streamer. If, for example, the lifetime of a current Streamer is 0.5 microsecond, the rise and fall times of the pulse may be approximately 0.1 microsecond. Accordingly, a voltage pulse is applied to electrode 22 which is efective to produce a great number of current streamers emanating outwardly from the electrode 22 in a uniform fashion throughout the cylindrical combustion chamber. At the end of the pulse, which may, for example, vary in duration between two or three microseconds, the sharp trailing edge of the pulse is effective to rapidly raise 'the potential of the electrode 22, relative to the space charge in the corona. This charge will, thus, be rapidly attracted back to the more positive electrode 22. It may be seen that, due to the inherent uniformity of a corona-type discharge, which will surround the electrode 22 uniformly over the volume of the combustion chamber 16, the sharp trailing edge of the pulse and the rapid reattraction of the corona space charge due thereto will produce a very ntense and highly uniform discharge in the area surrounding the electrode 22. vIt is 'this discharge which is used to ignite the fuel which has been introduced into the combustion chamber 16 through the valve 21. It is to be understood that proper timing between the piston travel, valve openings and electrode energization may be provided in substantially the conventional manner.

This invention has been described with reference to a particular embodiment thereof, and it is contemplated that various modifications and changes may be apparent to those skilled in the art. For example, other means for providing suitable voltage pulses may be provided. Additionally, it may be desirable to employ positive voltage pulses rather than the negative voltage pulses as described herein. A further modification which may be made to the present invention without departing from the spirit and scope thereof is to introduce a small gap into the electrode 22 for the purpose of limiting the corona discharge to a specific portion of the electrode, thus, reducing the power consumption. These and other modifications as will be apparent to those skilled in the art are within the scope of the present invention as defined by the appended claims.

What is claimed is: w

l. In combination with a rcciprocating internal combustion engine:

conductive means forming a combustion chamber of predetermined geometry; .f

an elongated cylindrical electrode of uniform cross-` section extending substantially through the combustion chamber; means to apply a voltage pulse across the electrode;

the predetermined geometry of the chamber being such that a non-uniform field is produced between the electrode and the chamber when a voltage pulse is applied whereby a corona discharge occurs unformly about the electrode.

2. In combination with an internal combustion engine having at least one reciprocating piston:

conductive means forming a combustion chamber of predetermined geometry;

an elongated cylindrical electrode of uniform crosssection extending substantially through the combustion chamber;

means to apply a rectangular voltage pulse of predetermined magnitude across the electrode;

the predetermined geometry of the chamber being such that a non-uniform field is produced between the electrode and the chamber when the rectangular voltage pulse of predetermined magnitude is applied whereby a corona discharge occurs uniformly about the electrode.

3. In combination with an internal combustion engine having a cylinder head and at least one rcciprocating piston:

conductive means including a portion of the cylinder head and a portion of the piston forming a combustion chamber of predetermined geometry when the piston is in a predetermined position;

an elongated cylindrical electrode of uniform crosssection extending substantially through the combustion chamber; means to apply a voltage pulse across the electrode when the piston is in the predetermined position;

the predetermined geometry of the chamber being such that a non-uniform field is produced between the electrode and the chamber when the voltage pulse is applied to the electrode whereby a corona discharge occurs uniformly about the electrode.

4. In combination with an internal combustion engine including a cylinder head and at least one reciprocating plston:

conductive means forming a substantially Semi-cylingricl groove in the inner surface of the cylinder conductive means forming a substantially Semi-cylindrical groove in the top surface of the piston;

the first and second Semi-cylindrical groove being relatively disposed so as to form a substantially cylindrical chamber intermediate the piston and the cylinder head;

the cylindrical chamber being communicable with a source of combustible fluid; an elongated cylindrical electrode of uniform crosssection disposed in concentric relation to and extending substantially through the cylindrical chamber;

means to apply a voltage pulse across the electrode whereby a corona discharge occurs uniformly about the electrode.

5. The combination as defined in claim 2 wherein the rise and fall times of the voltage pulses applied to the electrode are substantially less than the lifetime of a typical Streamer current in the corona discharge,

and the duration of the pulse is substantially greater than the lifetime of a typical Streamer current.

6. In combination with an internal combustion engine having at least one reciprocating piston:

conductive means forming a substantially cylindrical combustion chamber transverse to the path of travel of said piston; an elongated cylindricall electrode of uniform crosssection extending substantially through the combustion chamber and having a diameter which is small relative to the diameter of the combustion chamber; means to apply a rectangular voltage pulse of predetermined magnitude across the electrode to produce a non-uniform field between the electrode and the Chamber Whereby a corona discharge occurs uniformly about the electrode.

7. In combination With an internal Combustion engine including a cylinder head and at least one reciprocating piston:

conductive means forming a substantially Semi-cylindrical groove in the inner surface of the cylinder head;

conductive means forming a substantially Semi-cylin-V drical groove in the top surface of the piston; the first and second semi-Cylindrical groove being relatively disposed so as to form a substantially cylini 8 i i driCal Chamber intermediate the piston and the cylinder head;

the cylindrical Chamber being communicable with a source of combustible uid;

an elongated cylindrical electrode of uniform crosssection having a diameter which is small relative to the diameter of the cylindrical Chamber and disposed in concentric relation to and extending substantially through the cylindrical Chamber;

means to apply a voltage pulse across the electrode whereby a Corona disCharge occurs uniformly about the electrode.

No references cited. 

1. IN COMBINATION WITH A RECIPROCATING INTERNAL COMBUSTION ENGINE: CONDUCTIVE MEANS FORMING A COMBUSTION CHAMBER OF PREDETERMINED GEOMETRY; AN ELONGATED CYLINDRICAL ELECTRODE OF UNIFORM CROSSSECTION EXTENDING SUBSTANTIALLY THROUGH THE COMBUSTION CHAMBER; MEANS TO APPLY A VOLTAGE PULSE ACROSS THE ELECTRODE; THE PREDETERMINED GEOMETRY OF THE CHAMBER BEING SUCH THAT A NON-UNIFORM FIELD IS PRODUCED BETWEEN THE ELECTRODE AND THE CHAMBER WHEN A VOLTAGE PULSE IS APPLIED WHEREBY A CORONA DISCHARGE OCCURS UNIFORMLY ABOUT THE ELECTRODE. 